Judge Cuno Tarfusser ruled that Mr Barasa should be arrested and tried to ensure that he did not "endanger the investigation or the proceedings, and to prevent him from continuing with the commission of the crime", the ICC said.

Kenya's Attorney-General Githu Muigai said the warrant would come under "judicial consideration" before it was enforced.

"During the judicial consideration of the legality of the warrant, the subject [Mr Barasa] is entitled to make representations to the court," he added.

ICC chief prosecutor Fatou Bensouda called on Kenya to immediately arrest and transfer Mr Barasa to The Hague.

There was "compelling evidence" that he tried to bribe someone he thought was a witness in Mr Ruto's trial, she said.

Mr Barasa was part of a network trying to "sabotage" the case, Ms Bensouda alleged.

The arrest warrant was issued in August but made public only on Wednesday, partly to act as a warning to others that they could not get away with interfering with witnesses, reports the BBC's Anna Holligan from The Hague.

If found guilty Mr Barasa could face up to five years in jail.

Mr Barasa's lawyer Nick Kaufman told Reuters it was surprising that the warrant had been unsealed before Mr Ruto's lawyers cross-examined witnesses.

He said it risked creating the impression that it was aimed at influencing the trial's progress, Reuters reports.

At Mr Ruto's trial, the first witness, an alleged survivor of an attack on a church, continued giving evidence.

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Media captionAnna Holligan explains why William Ruto is in court, in 60 seconds

The court was in closed session, with extra protection for the female witness after unprecedented attempts to expose her identity, our correspondent says.

She is said to have survived the attack on the Kiambaa Church in Kenya's Rift Valley region after the December 2007 election, marred by allegations of widespread rigging.

About 36 people were burnt to death in the attack, blamed on supporters of Mr Ruto.

The trial resumed on Wednesday after it was adjourned last week to allow Mr Ruto to return to Kenya to deal with the 21 September attack on the Westgate shopping centre in the capital, Nairobi.

The Somali Islamist group, al-Shabab, said it carried out the four-day siege, which left 67 people dead while a further 39 are still missing.

Radio executive Joshua arap Sang is standing trial alongside Mr Ruto, accused of whipping up ethnic hatred in the aftermath of the election.

He has pleaded not guilty.

Some 1,200 people died and 600,000 were forced from their homes during the conflict.

Mr Ruto is the first senior government official to be tried by the ICC.

He and Mr Kenyatta were on opposite sides in the 2007 election, but formed an alliance to win power in elections in March this year.

They said their alliance showed that Kenyans had resolved their differences, and the ICC was meddling in the country's affairs by pressing ahead with their trials.